Fuel for fuel cell system

ABSTRACT

The present invention relates to a fuel for a fuel cell system comprising 5 vol. % or more of hydrocarbons based on the whole fuel, and 0.5-20 mass % of oxygenates in terms of an oxygen content based on the whole fuel, wherein the content of hydrocarbon compounds having a carbon number of 4 is 15 vol. % or less, the content of hydrocarbon compounds having a carbon number of 5 is 5 vol. % or more, the content of hydrocarbon compounds having a carbon number of 6 is 10 vol. % or more, the content of hydrocarbon compounds having carbon numbers of 7 and 8 in total is 20 vol. % or more, and the content of hydrocarbon compounds having carbon numbers of 10 or more is 20 vol. % or less.

TECHNICAL FIELD

[0001] The present invention relates to a fuel to be used for a fuelcell system.

BACKGROUND ART

[0002] Recently, with increasing awareness of the critical situation offuture global environments, it has been highly expected to develop anenergy supply system harmless to the global environments. Especiallyurgently required are to reduce CO₂ to prevent global warming and reduceharmful emissions such as THC (unreacted hydrocarbons in an exhaustgas), NO_(x), PM (particulate matter in an exhaust gas: soot, unburnedhigh boiling point and high molecular weight fuel and lubricating oil).Practical examples of such a system are an automotive power system toreplace a conventional Otto/Diesel engine and a power generation systemto replace thermal power generation.

[0003] Hence, a fuel cell, which has high energy efficiency and emitsbasically only H₂O and CO₂, has been regarded as a most expectativesystem to respond to social requests. In order to achieve such a system,it is necessary to develop not only the hardware but also the optimumfuel.

[0004] Conventionally, as a fuel for a fuel cell system, hydrogen,methanol, and hydrocarbons have been candidates.

[0005] As a fuel for a fuel cell system, hydrogen is advantageous in apoint that it does not require reformer, however, because of a gas phaseat a normal temperature, it has difficulties in storage and loading in avehicle and special facilities are required for its supply. Further, therisk of inflammation is high and therefore, it has to be handledcarefully.

[0006] On the other hand, methanol is advantageous in a point that it isrelatively easy to reform, however power generation quantity per weightis low and owing to its toxicity, handling has to be careful. Further,it has a corrosive property, special facilities are required for itsstorage and supply.

[0007] Like this, a fuel to sufficiently utilize the performances of afuel cell system has not yet been developed. Especially, as a fuel for afuel cell system, the following are required: power generation quantityper weight is high; power generation quantity per CO₂ emission is high;a fuel consumption is low in a fuel cell system as a whole; anevaporative gas (evapo-emission) is a little; deterioration of a fuelcell system comprising such as a reforming catalyst, a water gas shiftreaction catalyst, a carbon monoxide conversion catalyst, fuel cellstacks and the like is scarce to keep the initial performances for along duration; a starting time for the system is short; and storagestability and handling easiness are excellent.

[0008] Incidentally, in a fuel cell system, it is required to keep afuel and a reforming catalyst at a proper temperature, the net powergeneration quantity of the entire fuel cell system is equivalent to thevalue calculated by subtracting the energy necessary for keeping thetemperature (the energy for keeping balance endothermic heat andexothermic reaction following the preheating energy) from the actualpower generation quantity. Consequently, if the temperature for thereforming is lower, the energy for preheating is low and that istherefore advantageous and further the system starting time isadvantageously shortened. In addition, it is also necessary that theenergy for preheating per fuel weight is low. If the preheating isinsufficient, unreacted hydrocarbon (THC) in an exhaust gas increasesand it results in not only decrease of the power generation quantity perweight but also possibility of becoming causes of air pollution. To sayconversely, when some kind of fuels are reformed by the same reformerand the same temperature it is more advantageous that THC in an exhaustgas is lower and the conversion efficiency to hydrogen is higher.

[0009] The present invention, taking such situation into consideration,aims to provide a fuel suitable for a fuel cell system satisfying theabove-described requirements in good balance.

DISCLOSURE OF THE INVENTION

[0010] Inventors of the present invention have extensively investigatedto solve the above-described problems and found that a fuel comprising aspecific amount of oxygenates (oxygen-containing compounds) is suitablefor a fuel cell system.

[0011] That is, a fuel for a fuel cell system according to the firstaspect of the invention comprises;

[0012] (1) 5 vol. % or more of hydrocarbons based on the whole fuel, and0.5-20 mass % of oxygenates in terms of an oxygen content based on thewhole fuel, wherein the content of hydrocarbon compounds having a carbonnumber of 4 is 15 vol. % or less, the content of hydrocarbon compoundshaving a carbon number of 5 is 5 vol. % or more, the content ofhydrocarbon compounds having a carbon number of 6 is 10 vol. % or more,the content of hydrocarbon compounds having carbon numbers of 7 and 8 intotal is 20 vol. % or more, and the content of hydrocarbon compoundshaving carbon numbers of 10 or more is 20 vol. % or less.

[0013] Further, the fuel for a fuel cell system according to the secondaspect of the invention comprises;

[0014] (2) 5 vol. % or more of hydrocarbons based on the whole fuel, and0.5-20 mass % of oxygenates in terms of an oxygen content based on thewhole fuel, wherein the fuel has distillation properties; the initialboiling point in distillation of 24° C. or more and 50° C. or less, the10 vol. % distillation temperature of 35° C. or more and 70° C. or less,the 90 vol. % distillation temperature of 100° C. or more and 180° C. orless, and the final boiling point in distillation of 130° C. or more and210° C. or less.

[0015] The fuel for a fuel cell system comprising the specific amount ofthe oxygenates is preferable to satisfy the following additionalrequirements;

[0016] (3) a sulfur content is 50 ppm by mass or less based on the wholefuel;

[0017] (4) saturates are 30 vol. % or more based on the wholehydrocarbons;

[0018] (5) olefins are 35 vol. % or less based on the wholehydrocarbons;

[0019] (6) aromatics are 50 vol. % or less based on the wholehydrocarbons;

[0020] (7) a ratio of paraffins in saturates is 60 vol. % or more;

[0021] (8) a ratio of branched paraffins in paraffins is 30 vol. % ormore;

[0022] (9) heat capacity of the fuel is 2.6 kJ/kg ° C. or less at 15° C.and 1 atm in liquid phase;

[0023] (10) heat of vaporization is 400 kJ/kg or less;

[0024] (11) Reid vapor pressure (RVP) is 10 kPa or more and less than100 kPa;

[0025] (12) research octane number (RON, the octane number by researchmethod) is 101.0 or less;

[0026] (13) oxidation stability is 240 minutes or longer; and

[0027] (14) density is 0.78 g/cm³ or less.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 shows a flow chart of a steam reforming type fuel cellsystem employed for evaluation of a fuel for a fuel cell system of theinvention. FIG. 2 is a flow chart of a partial oxidation type fuel cellsystem employed for evaluation of a fuel for a fuel cell system of theinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0029] Hereinafter, the contents of the invention will be describedfurther in detail.

[0030] In the present invention, the content of hydrocarbons is requiredto be 5 vol. % or more based on the whole fuel in view of a high powergeneration quantity per weight and a high power generation quantity perCO₂ emission.

[0031] In the present invention, the oxygenates mean alcohols havingcarbon numbers of 2-4, ethers having carbon numbers of 2-8 and the like.More particularly, the oxygenates include methanol, ethanol, dimethylether, methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether,tertiary amyl methyl ether (TAME), tertiary amyl ethyl ether and thelike.

[0032] The content of these oxygenates is required to be 0.5 mass % ormore in terms of an oxygen content based on the whole fuel in view of alow fuel consumption of a fuel cell system as a whole, a low THC in anexhaust gas, short starting time of a system and the like, and furtheris required to be 20 mass % or below and most preferably 3 mass % orbelow taking into consideration of a balance between a high powergeneration quantity per weight and a high power generation quantity perCO₂ emission.

[0033] In the first aspect of the invention, the content of hydrocarboncompounds having the specific carbon atoms is necessary for thefollowing requirements.

[0034] The content of hydrocarbon compounds having a carbon number of 4(V (C₄)) shows the content of hydrocarbon compounds having 4 carbonatoms based on the whole hydrocarbons and is required to be 15 vol. % orless since the evaporative gas (evapo-emission) can be suppressed to lowand the handling property is good in view of inflammability or the likeand preferably 10 vol. % or less and most preferably 5 vol. % or less.

[0035] The content of hydrocarbon compounds having a carbon number of 5(V (C₅)) shows the content of hydrocarbon compounds having 5 carbonatoms based on the whole hydrocarbons and is required to be 5 vol. % ormore in view of a high power generation quantity per weight, a highpower generation quantity per CO₂ emission, and a low fuel consumptionof a fuel cell system as a whole and preferably 10 vol. % or more, morepreferably 15 vol. % or more, further more preferably 20 vol. % or more,much further more preferably 25 vol. % or more, and most preferably 30vol. % or more.

[0036] The content of hydrocarbon compounds having a carbon number of 6(V (C₆)) shows the content of hydrocarbon compounds having 6 carbonatoms based on the whole hydrocarbons and is required to be 10 vol. % ormore in view of a high power generation quantity and a low fuelconsumption of a fuel cell system as a whole and preferably 15 vol. % ormore, more preferably 20 vol. % or more, further more preferably 25 vol.% or more, and most preferably 30 vol. % or more.

[0037] Further, the content of hydrocarbon compounds having carbonnumbers of 7 and 8 (V (C₇+C₈)) in total shows the content of hydrocarboncompounds having 7 and 8 carbon atoms in total based on the wholehydrocarbons and is required to be 20 vol. % or more because of a highpower generation quantity per weight, a high power generation quantityper CO₂ emission, and a low fuel consumption of a fuel cell system as awhole and preferably 25 vol. % or more, more preferably 35 vol. % ormore, and most preferably 40 vol. % or more.

[0038] Further, in the invention, the content of hydrocarbons havingcarbon numbers of 10 or more is not particularly restricted, however,because of a high power generation quantity per CO₂ emission, a low fuelconsumption of a fuel cell system as a whole, and small deterioration ofa reforming catalyst to maintain initial performances for a longduration, the total amount of hydrocarbon compounds having a carbonnumber of 10 or more (V (C₁₀₊) based on the whole hydrocarbons isrequired to be 20 vol. % or less, preferably 10 vol. % or less, and mostpreferably 5 vol. % or less.

[0039] Incidentally, the above-described V (C₄), V (C₅), V (C₆), V(C₇+C₈), and V (C₁₀₊) are values quantitatively measured by thefollowing gas chromatography. That is, these values are measured inconditions: employing capillary columns of methyl silicon for columns;using helium or nitrogen as a carrier gas; employing a hydrogenionization detector (FID) as a detector; the column length of 25 to 50m; the carrier gas flow rate of 0.5 to 1.5 ml/min, the split ratio of(1:50) to (1:250); the injection inlet temperature of 150 to 250° C.;the initial column temperature of −10 to 10° C.; the final columntemperature of 150 to 250° C., and the detector temperature of 150 to250° C.

[0040] In the second aspect of the invention, the distillationproperties are as follows.

[0041] The initial boiling point (initial boiling point 0) of a fuel is24° C. or higher and 50° C. or lower, preferably 27° C. or higher andmore preferably 30° C. or higher. The 10 vol. % distillation temperature(T₁₀) is 35° C. or higher and 70° C. or lower, preferably 40° C. orhigher and more preferably 45° C. or higher. The 90 vol. % distillationtemperature (T₉₀) is 100° C. or higher and 180° C. or lower andpreferably 170° C. or lower. The final boiling point in distillation is130° C. or higher and 210° C. or lower and preferably 200° C. or lower.

[0042] If the initial boiling point (initial boiling point 0) indistillation is low, the fuel is highly inflammable and an evaporativegas (THC) is easy to be generated and there is a problem to handle thefuel. Similarly regarding to the 10 vol. % distillation temperature(T₁₀), if it is less than the above-described restricted value, the fuelis highly inflammable and an evaporative gas (THC) is easy to begenerated and there is a problem to handle the fuel.

[0043] On the other hand, the upper limit values of the 90 vol. %distillation temperature (T₉₀) and the final boiling point indistillation are determined in view of a high power generation quantityper weight, a high power generation quantity per CO₂ emission, a lowfuel consumption of a fuel cell system as a whole, a low THC in anexhaust gas, short starting time of a system, small deterioration of areforming catalyst to retain the initial properties, and the like.

[0044] Further, the 30 vol. % distillation temperature (T₃₀), 50 vol. %distillation temperature (T₅₀), and 70 vol. % distillation temperature(T₇₀) of the fuel of the invention are not particularly restricted,however, the 30 vol. % distillation temperature (T₃₀) is preferably 50°C. or higher and 100° C. or lower, the 50 vol. % distillationtemperature (T₅₀) is preferably 60° C. or higher and 120° C. or lower,and the 70 vol. % distillation temperature (T₇₀) is 80° C. or higher and150° C. or lower.

[0045] Incidentally, the above-described initial boiling point (initialboiling point 0) in distillation, the 10 vol. % distillation temperature(T₁₀), the 30 vol. % distillation temperature (T₃₀), the 50 vol. %distillation temperature (T₅₀), the 70 vol. % distillation temperature(T₇₀), the 90 vol. % distillation temperature (T₉₀), and the finalboiling point in distillation are distillation properties measured byJIS K 2254, “Petroleum products-Determination of distillationcharacteristics”.

[0046] Further, the content of sulfur in a fuel of the invention is notparticularly restricted, however, because deterioration of a fuel cellsystem comprising such as a reforming catalyst, a water gas shiftreaction catalyst, a carbon monoxide removal catalyst, fuel cell stacks,and the like can be suppressed to low and the initial performances canbe maintained for a long duration, the content is preferably 50 ppm bymass or less, more preferably 30 ppm by mass or less, further morepreferably 10 ppm by mass or less, much further more preferably 1 ppm bymass or less, and most preferably 0.1 ppm by mass or less.

[0047] Here, sulfur means sulfur measured by JIS K 2541, “Crude Oil andPetroleum Products-Determination of sulfur content”, in case of 1 ppm bymass or more and means sulfur measured by ASTM D4045-96, “Standard TestMethod for Sulfur in Petroleum Products by Hydrogenolysis andRateometric Colorimetry” in the case of less than 1 ppm by mass.

[0048] In the invention, the respective contents of saturates, olefinsand aromatics are not particularly restricted, however, saturates (V(S)), olefins (V (O)) and aromatics (V (Ar)) are preferably 30 vol. % ormore, 35 vol. % or less, and 50 vol. % or less, respectively based onthe whole hydrocarbons. Hereinafter, these compounds will separately bedescribed.

[0049] In view of a high power generation quantity per weight, a highpower generation quantity per CO₂ emission, a low fuel consumption of afuel cell system as a whole, small THC in an exhaust gas, and a shortstarting time of the system, V (S) is preferably 30 vol. % or more, morepreferably 40 vol. % or more, further more preferably 50 vol. % or more,much further more preferably 60 vol. % or more, much further morepreferably 70 vol. % or more, much further more preferably 80 vol. % ormore, much further more preferably 90 vol. % or more, and mostpreferably 95 vol. % or more.

[0050] In view of a high power generation quantity per weight, a highpower generation quantity per CO₂ emission, small deterioration of areforming catalyst to maintain the initial performances for a longduration, and a good storage stability, V (O) is preferably 35 vol. % orless, more preferably 25 vol. % or less, further more preferably 20 vol.% or less, much further more preferably 15 vol. % or less, and mostpreferably 10 vol. % or less based on the whole hydrocarbons.

[0051] In view of a high power generation quantity per weight, a highpower generation quantity per CO₂ emission, a low fuel consumption of afuel cell system as a whole, small THC in an exhaust gas, a shortstarting time of the system, and small deterioration of a reformingcatalyst to maintain the initial performances for a long duration, V(Ar) is preferably 50 vol. % or less, more preferably 45 vol. % or less,further more preferably 40 vol. % or less, much further more preferably35 vol. % or less, much further more preferably 30 vol. % or less, muchfurther more preferably 20 vol. % or less, much further more preferably10 vol. % or less, and most preferably 5 vol. % or less.

[0052] Further, it is most preferable to satisfy the above-describedpreferable ranges of sulfur and the above-described preferable rangesfor the aromatics since deterioration of a reforming catalyst can besuppressed to low and the initial performances can be maintained for along duration.

[0053] The values of the above-described V (S), V (O), and V (Ar) areall measured value according to the fluorescent indicator adsorptionmethod of JIS K 2536, “Liquid petroleum products-Testing method ofcomponents”.

[0054] Further, in the invention, the ratio of paraffins in saturates ofa fuel is not particularly restricted, however, because of a high H₂generation quantity, a high power generation quantity per weight, a highpower generation quantity per CO₂ emission and the like, the ratio ofparaffins in saturates is preferably 60 vol. % or more, more preferably65 vol. % or more, further more preferably 70 vol. % or more, muchfurther more preferably 80 vol. % or more, much further more preferably85 vol. % or more, much further more preferably 90 vol. % or more, andmost preferably 95 vol. % or more.

[0055] The above-described saturates and paraffins are valuesquantitatively measured by the gas chromatography method mentionedabove.

[0056] Further, the ratio of branched paraffins in the above-describedparaffins is not particularly restricted, however, the ratio of branchedparaffins in paraffins is preferably 30 vol. % or more, more preferably50 vol. % or more, and most preferably 70 vol. % or more because of ahigh power generation quantity per weight, a high power generationquantity per CO₂ emission, a low fuel consumption of a fuel cell systemas a whole, small THC in an exhaust gas, and a short starting time ofthe system.

[0057] The amounts of the above-described paraffins and branchedparaffins are values quantitatively measured by the gas chromatographymethod mentioned above.

[0058] Further, in the invention, the heat capacity of a fuel is notparticularly restricted, however, the heat capacity is preferably 2.6kJ/kg·° C. or less at 15° C. and 1 atm in liquid phase in view of a lowfuel consumption of a fuel cell system as a whole.

[0059] Further, in the invention, the heat of vaporization of a fuel isnot particularly restricted, the heat of vaporization is preferably 400kJ/kg or less because of a low fuel consumption of a fuel cell system asa whole.

[0060] Those heat capacity and heat of vaporization can be calculatedfrom the contents of respective components quantitatively measured bythe above-described gas chromatography and the numeric values per unitweight of the respective components disclosed in “Technical DataBook-Petroleum Refining”, Vol. 1, Chap. 1, General Data, Table 1C1.

[0061] Further, in the invention, the Reid vapor pressure (RVP) of afuel is not particularly restricted, however, it is preferably 10 kPa ormore in relation to the power generation quantity per weight andpreferably less than 100 kPa in relation to suppression of the amount ofan evaporative gas (evapo-emission). It is more preferably 20 kPa ormore and less than 90 kPa, further more preferably 40 kPa or more andless than 75 kPa, and most preferably 40 kPa or more and less than 60kPa. Here, the Reid vapor pressure (RVP) means the vapor pressure (Reidvapor pressure (RVP)) measured by JIS K 2258, “Testing method for VaporPressure of Crude Oil and Products (Reid Method)”.

[0062] Further, in the invention, the research octane number (RON, theoctane number by research method) is not particularly restricted,however, it is preferably 101.0 or less since deterioration of areforming catalyst can be suppressed to low and the initial performancesof a reforming catalyst can be maintained for a long duration owing to ahigh power generation quantity per weight, a low fuel consumption of afuel cell system as a whole, small THC in an exhaust gas, and a shortstarting time of the system. Here, the octane number by research method(RON) means the research method octane number measured by JIS K 2280,“Petroleum products-Fuels-Determination of octane number, cetane numberand calculation of cetane index”.

[0063] Further, in the invention, the oxidation stability of a fuel isnot particularly restricted, however, it is preferably 240 minutes orlonger in view of storage stability. Here, the oxidation stability isthe oxidation stability measured according to JIS K 2287, “TestingMethod for Oxidation Stability of Gasoline (Induction Period Method)”.

[0064] Further, in the invention, the density of a fuel is notparticularly restricted, however, it is preferably 0.78 g/cm³ or lesssince deterioration of a reforming catalyst can be suppressed to low andthe initial performances of a reforming catalyst can be maintained for along duration owing to small THC in an exhaust gas and a short startingtime of the system. Here, the density means the density measuredaccording to JIS K 2249, “Crude petroleum and petroleumproducts-Determination of density and petroleum measurement tables basedon a reference temperature(15° C.)38 .

[0065] A production method of the fuel of the invention is notparticularly restricted. Practical method is, for example, the fuel canbe produced by one or more kinds of oxygenates and further by mixinghydrocarbons at need.

[0066] As for hydrocarbons, for example, the hydrocarbons can beprepared by blending one or more following hydrocarbon base materials;light naphtha obtained by the atmospheric distillation of crude oil,heavy naphtha obtained by the atmospheric distillation of crude oil,desulfurized light naphtha obtained by desulfurization of light naphtha,desulfurized heavy naphtha obtained by desulfurization of heavy naphtha,desulfurized full-range naphtha B obtained by desulfurization of naphthafraction obtained by distillation of crude oil, isomerate obtained byconverting light naphtha into isoparaffins by an isomerization process,alkylate obtained by the addition reaction (alkylation) of low moleculeweight olefins to hydrocarbons such as isobutane, desulfurized alkylateobtained by desulfurizing alkylate, low sulfur alkylate produced fromdesulfurized hydrocarbons such as isobutane and desulfurized lowmolecule weight olefins, reformate obtained by catalytic reforming,raffinate which is residue after extraction of aromatics from reformate,light distillate of reformate, middle to heavy distillate of reformate,heavy distillate of reformate, cracked gasoline obtained by catalyticcracking or hydrocracking process, light distillate of cracked gasoline,heavy distillate of cracked gasoline, desulfurized cracked gasolineobtained by desulfurizing cracked gasoline, desulfurized lightdistillate of cracked gasoline obtained by desulfurizing lightdistillate of cracked gasoline, desulfurized heavy distillate of crackedgasoline obtained by desulfurizing heavy distillate of cracked gasoline,a light distillate of “GTL (Gas to Liquids)” obtained by F-T(Fischer-Tropsch) synthesis after cracking natural gas or the like tocarbon monoxide and hydrogen, desulfurized LPG obtained by desulfurizingLPG, and the like. The fuel can also be produced by desulfurizing byhydrotreating or adsorption after mixing one or more types of the abovebase materials.

[0067] Among them, preferable materials as the base materials for theproduction of the fuel of the invention are light naphtha, desulfurizedlight naphtha, isomerate, desulfurized alkylates obtained bydesulfurizing alkylates, low sulfur alkylates produced from desulfurizedhydrocarbons such as isobutane and desulfurized low molecule weightolefins, desulfurized light distillate of cracked gasoline obtained bydesulfurizing a light distillate of cracked gasoline, a light distillateof GTL, desulfurized LPG obtained by desulfurizing LPG, and the like.

[0068] A fuel for a fuel cell system of the invention may compriseadditives such as dyes for identification, oxidation inhibitors forimprovement of oxidation stability, metal deactivators, corrosioninhibitors for corrosion prevention, detergents for keeping cleanness ofa fuel system, lubricity improvers for improvement of lubricatingproperty and the like.

[0069] However, since a reforming catalyst is to be scarcelydeteriorated and the initial performances are to be maintained for along duration, the amount of dyes is preferably 10 ppm or less and morepreferably 5 ppm or less. For the same reasons, the amount of oxidationinhibitors is preferably 300 ppm or less, more preferably 200 ppm orless, further more preferably 100 ppm or less, and most preferably 10ppm or less. For the same reasons, the amount of metal deactivators ispreferably 50 ppm or less, more preferably 30 ppm or less, further morepreferably 10 ppm or less, and most preferably 5 ppm or less. Further,similarly since a reforming catalyst is to be scarcely deteriorated andthe initial performances are to be maintained for a long duration, theamount of corrosion inhibitors is preferably 50 ppm or less, morepreferably 30 ppm or less, further more preferably 10 ppm or less, andmost preferably 5 ppm or less. For the same reasons, the amount ofdetergents is preferably 300 ppm or less, more preferably 200 ppm orless, and most preferably 100 ppm or less. For the same reasons, theamount of lubricity improvers is preferably 300 ppm or less, morepreferably 200 ppm or less, and most preferably 100 ppm or less.

[0070] A fuel of the invention is to be employed as a fuel for a fuelcell system. A fuel cell system mentioned herein comprises a reformerfor a fuel, a carbon monoxide conversion apparatus, fuel cells and thelike, however, a fuel of the invention may be suitable for any fuel cellsystem.

[0071] The reformer is an apparatus for obtaining hydrogen, by reforminga fuel. Practical examples of the reformer are:

[0072] (1) a steam reforming type reformer for obtaining products ofmainly hydrogen by treating a heated and vaporized fuel and steam with acatalyst such as copper, nickel, platinum, ruthenium and the like;

[0073] (2) a partial oxidation type reformer for obtaining products ofmainly hydrogen by treating a heated and vaporized fuel and air with orwithout a catalyst such as copper, nickel, platinum, ruthenium and thelike; and

[0074] (3) an auto thermal reforming type reformer for obtainingproducts of mainly hydrogen by treating a heated and vaporized fuel,steam and air, which carries out the partial oxidation of (2) in theprior stage and carries out the steam type reforming of (1) in theposterior stage while using the generated heat of the partial oxidationreaction with a catalyst such as copper, nickel, platinum, ruthenium andthe like.

[0075] The carbon monoxide conversion apparatus is an apparatus forremoving carbon monoxide which is contained in a gas produced by theabove-described reformer and becomes a catalyst poison in a fuel celland practical examples thereof are:

[0076] (1) a water gas shift reactor for obtaining carbon dioxide andhydrogen as products from carbon monoxide and steam by reacting areformed gas and steam in the presence of a catalyst of such as copper,nickel, platinum, ruthenium and the like; and

[0077] (2) a preferential oxidation reactor for converting carbonmonoxide into carbon dioxide by reacting a reformed gas and compressedair in the presence of a catalyst of such as platinum, ruthenium and thelike, and these are used singly or jointly.

[0078] As a fuel cell, practical examples are a proton exchange membranetype fuel cell (PEFC), a phosphoric acid type fuel cell (PAFC), a moltencarbonate type fuel cell (MCFC), a solid oxide type fell cell (SOFC) andthe like.

[0079] Further, the above-described fuel cell system can be employed foran electric automobile, a hybrid automobile comprising a conventionalengine and electric power, a portable power source, a dispersion typepower source, a power source for domestic use, a cogeneration system andthe like.

EXAMPLES

[0080] The properties of base materials employed for the respectivefuels for examples and comparative examples are shown in Tables 1 and 2.

[0081] Also, the properties of the respective fuels employed forexamples and comparative examples are shown in Table 3. TABLE 1desulfur- desulfur- light middle to ized full- ized full- distillateheavy range range of distillate naphtha naphtha B reformate of *1 *2 *3reformate sulfur 0.3 0.3 0.2 0.4 hydrocarbon ratio carbon number: C₄vol. % 1.6 0.2 18.0 0.0 carbon number: C₅ vol. % 12.5 9.5 49.9 0.0carbon number: C₆ vol. % 19.7 22.5 31.9 0.6 carbon number: C₇ vol. %20.9 22.3 0.2 36.2 carbon number: C₈ vol. % 24.3 24.4 0.0 47.9 carbonnumber: C_(7 + C) ₈ vol. % 45.2 46.7 0.2 84.1 carbon number: C₉ vol. %18.5 18.6 0.0 13.3 carbon number: C₁₀₊ vol. % 2.5 2.5 0.0 2.0composition saturates vol. % 92.8 94.4 97.2 4.5 olefins vol. % 0.6 0.81.8 0.1 aromatics vol. % 6.6 4.8 1.1 95.4 paraffins in saturates vol. %85.5 87.3 99.0 98.4 branched paraffins in vol. % 44.4 45.0 62.9 48.4paraffins oxygen mass % 0.0 0.0 0.0 0.0 distillation initial boilingpoint ° C. 35.0 42.0 22.0 102.5 10% point ° C. 55.0 59.5 26.0 117.5 30%point ° C. 73.5 75.5 32.5 123.0 50% point ° C. 91.5 92.0 40.5 129.5 70%point ° C. 112.5 111.5 47.5 137.5 90% point ° C. 134.5 135.0 54.0 151.0final boiling point ° C. 155.5 152.5 66.0 191.5 heat capacity kJ/kg · °C. 2.105 2.113 2.230 1.715 (liquid) heat capacity (gas) kJ/kg · ° C.1.523 1.536 1.586 1.172 heat of vaporization kJ/kg 317.2 324.7 348.1344.4 RVP kPa 66.9 58.6 127.5 7.0 research octane 63.4 60.1 78.2 111.5number oxidation stability min. >1440 >1440 >1440 >1440 density g/cm³0.7085 0.7112 0.6487 0.8621 net heat of kJ/kg 44225 44267 44974 41024combustion cracked desulfurized cracked light cracked gasoline gasolinelight alkylate *5 *6 gasoline *7 *8 sulfur 80 7 0.7 8 hydrocarbon ratiocarbon number: C₄ vol. % 7.3 13.4 13.2 8.6 carbon number: C₅ vol. % 25.147.1 47.0 3.2 carbon number: C₆ vol. % 20.1 29.2 29.9 2.8 carbon number:C₇ vol. % 18.1 8.8 8.7 2.5 carbon number: C₈ vol. % 13.7 1.4 1.2 79.8carbon number: C₇ + C₈ vol. % 31.8 10.2 9.9 82.3 carbon number: C₉ vol.% 11.4 0.0 0.0 1.1 carbon number: C₁₀₊ vol. % 4.3 0.0 0.0 2.0composition saturates vol. % 47.2 45.0 46.5 99.8 olefins vol. % 39.453.7 52.3 0.1 aromatics vol. % 13.4 1.3 1.2 0.1 paraffins in saturatesvol. % 85.6 93.5 94.0 100.0 branched paraffins in vol. % 88.6 86.1 86.391.3 paraffins oxygen mass % 0.0 0.0 0.0 0.0 distillation initialboiling point ° C. 31.5 24.5 24.5 31.0 10% point ° C. 51.5 32.5 31.071.5 30% point ° C. 77.0 38.5 37.5 98.5 50% point ° C. 111.5 45.0 44.5105.5 70% point ° C. 150.5 53.5 53.5 110.0 90% point ° C. 189.0 69.569.0 122.5 final boiling point ° C. 216.5 93.5 92.0 181.5 heat capacity(liquid) kJ/kg · ° C. 2.063 2.159 2.167 2.071 heat capacity (gas) kJ/kg· ° C. 1.464 1.519 1.523 1.590 heat of vaporization kJ/kg 333.2 353.2352.7 289.8 RVP kPa 62.5 115.3 115.8 58.5 research octane 92.3 95.5 95.095.6 number oxidation stability min. 210 150 150 >1440 density g/cm³0.7388 0.6601 0.6590 0.6955 net heat of kJ/kg 43903 44589 44555 44488combustion

[0082] TABLE 2 low sulfur GTL alkylate naphtha desulfurized *9 *10 LPG*11 MTBE sulfur 0.1 0.1 0.4 0.1 hydrocarbon ratio carbon number: C₄ vol.% 8.4 2.1 98.0 — carbon number: C₅ vol. % 3.3 12.4 0.1 — carbon number:C₆ vol. % 2.9 19.7 0.0 — carbon number: C₇ vol. % 2.4 21.0 0.0 — carbonnumber: C₈ vol. % 80.2 23.6 0.0 — carbon number: C₇ + C₈ vol. % 82.644.6 0.0 — carbon number: C₉ vol. % 0.9 17.7 0.0 — carbon number: C₁₀₊vol. % 1.9 3.5 0.0 — composition saturates vol. % 99.7 100.0 99.5 —olefins vol. % 0.2 0.0 0.5 — aromatics vol. % 0.1 0.0 0.0 — paraffins insaturates vol. % 100.0 100.0 100.0 — branched paraffins in vol. % 91.453.5 34.6 — paraffins oxygen mass % 0.0 0.0 0.0 18.2 distillationinitial boiling point ° C. 30.5 31.5 — 55.0 10% point ° C. 71.0 47.5 — —30% point ° C. 99.0 69.5 — — 50% point ° C. 105.0 92.5 — — 70% point °C. 110.5 113.5 — — 90% point ° C. 121.5 129.5 — — final boiling point °C. 177.0 150.5 — — heat capacity kJ/kg · ° C. 2.071 2.167 2.369 2.075heat capacity (gas) kJ/kg · ° C. 1.594 1.590 1.628 1.477 heat ofvaporization kJ/kg 290.8 309.5 379.6 319.7 RVP kPa 59.5 72.3 339.0 53.0research octane 95.4 51.5 95.0 118.0 number oxidation stabilitymin. >1440 >1440 — — density g/cm³ 0.6951 0.6825 0.5776 0.7456 net heatof kJ/kg 44501 44576 45689 35171 combustion ethanol methanol DME *12sulfur 0.1 0.1 0.1 hydrocarbon ratio carbon number: C₄ vol. % — — —carbon number: C₅ vol. % — — — carbon number: C₆ vol. % — — — carbonnumber: C₇ vol. % — — — carbon number: C₈ vol. % — — — carbon number:C₇ + C₈ vol. % — — — carbon number: C₉ vol. % — — — carbon number: C₁₀₊vol. % — — — composition saturates vol. % — — — olefins vol. % — — —aromatics vol. % — — — paraffins in saturates vol. % — — — branchedparaffins in vol. % — — — paraffins oxygen mass % 34.8 49.9 34.8distillation initial boiling point ° C. 78.0 64.7 −25.0 10% point ° C. —— — 30% point ° C. — — — 50% point ° C. — — — 70% point ° C. — — — 90%point ° C. — — — final boiling point ° C. — — — heat capacity (liquid)kJ/kg · ° C. 2.339 2.456 2.510 heat capacity (gas) kJ/kg · ° C. 1.3811.343 1.389 heat of vaporization kJ/kg 855.6 1096.8 467.8 RVP kPa 15.930.0 843.2 research octane 130.0 110.0 — number oxidation stability min.— — density g/cm³ 0.7963 0.7961 0.6709 net heat of kJ/kg 26824 1991628840 combustion

[0083] TABLE 3 EX. 1 Ex. 2 EX. 3 EX. 4 Mixing desulfurized LPG 2% ratiodesulfurized full-range naphtha 94% Component desulfurized full-rangenaphtha B GTL naphtha 91% alkylate 20% low sulfur alkylate 20% crackedlight gasoline 30% cracked gasoline desulfurized cracked light gasoline30% light distillate of reformate 3% 3% middle to heavy distillate ofreformate 30% 30% methanol 6% ethanol 9% MTBE 15% 15% DME 2% PropertiesSulfur ppm by mass 0.3 0.1 3.5 0.4 ratio by carbon number carbon number:C₄ vol. % 1.6 2.1 7.6 9.5 carbon number: C₅ vol. % 12.5 12.4 19.6 19.2carbon number: C₆ vol. % 19.7 19.7 12.7 12.6 carbon number: C₇ vol. %20.9 21.0 16.9 16.5 carbon number: C₈ vol. % 24.3 23.6 37.0 36.1 carbonnumber: C₇ + C₈ vol. % 45.2 44.6 53.9 52.7 carbon number: C₉ vol. % 18.517.7 5.1 4.9 carbon number: C₁₀₊ vol. % 2.5 3.5 1.2 1.2 Compositionsaturates vol. % 92.8 100.0 45.4 47.2 olefins vol. % 0.0 0.0 19.5 18.6aromatics vol. % 6.6 0.0 35.1 34.2 paraffins in saturates vol. % 85.5100.0 97.6 97.8 branched paraffins in vol. % 44.4 53.5 85.7 83.2paraffins Oxygen mass % 3.3 3.6 3.4 2.8 Density g/cm³ 0.7138 0.69270.7405 0.7382 Distillation properties initial boiling point ° C. 35.031.0 28.5 29.0 10% point ° C. 51.0 16.5 50.5 50.0 30% point ° C. 65.568.0 67.5 68.0 50% point ° C. 85.0 84.5 89.5 89.0 70% point ° C. 104.0103.0 106.0 105.0 90% point ° C. 129.5 122.0 125.5 125.0 final boilingpoint ° C. 150.0 145.5 160.5 158.0 Reid vapor pressure kPa 80 77 76 77Research octane number 68.9 59.2 99.3 99.5 Oxidation stability min. 1440or 1440 or 1440 or 1440 or more more more more Net heat of combustionkJ/kg 42598 42740 41627 41915 Heat capacity (liquid) kJ/kg · ° C. 2.1282.185 1.983 1.982 Heat capacity (gas) kJ/kg · ° C. 1.511 1.568 1.4041.410 Heat of vaporization kJ/kg 369.3 366.0 335.1 333.4 EX. 5 Comp. Ex.1 Comp. Ex. 2 Mixing desulfurized LPG ratio desulfurized full-rangenaphtha 10% 100% desulfurized full-range naphtha B 95% GTL naphthaalkylate low sulfur alkylate cracked light gasoline cracked gasolinedesulfurized cracked light gasoline light distillate of reformate middleto heavy distillate of reformate methanol 90% ethanol MTBE 5% DMEProperties Sulfur ppm by mass 0.3 0.1 0.3 ratio by carbon number carbonnumber: C₄ vol. % 0.2 1.6 1.6 carbon number: C₅ vol. % 95 12.5 12.5carbon number: C₆ vol. % 22.5 19.7 19.7 carbon number: C₇ vol. % 22.320.9 20.9 carbon number: C₈ vol. % 24.4 24.3 24.3 carbon number: C₇ + C₈vol. % 46.7 45.2 45.2 carbon number: C₉ vol. % 18.6 18.5 18.5 carbonnumber: C₁₀₊ vol. % 2.5 2.5 2.5 Composition saturates vol. % 94.4 92.892.8 olefins vol. % 0.8 0.0 0.6 aromatics vol. % 4.8 6.6 6.6 paraffinsin saturates vol. % 87.3 85.5 85.5 branched paraffins in vol. % 45.044.4 44.4 paraffins Oxygen mass % 1.0 45.4 0.0 Density g/cm³ 0.71290.7873 0.7085 Distillation properties initial boiling point ° C. 41.035.0 35.0 10% point ° C. 57.0 55.0 55.0 30% point ° C. 71.0 64.5 73.550% point ° C. 91.0 65.0 91.5 70% point ° C. 111.0 65.5 112.5 90% point° C. 134.5 72.5 134.5 final boiling point ° C. 152.0 125.5 155.5 Reidvapor pressure kPa 59 — 67 Research octane number 62.8 — 63.4 Oxidationstability min. 1441 or 1440 or 1440 or more more more Net heat ofcombustion kJ/kg 43791 22103 44230 Heat capacity (liquid) kJ/kg · ° C.2.111 2.424 2.105 Heat capacity (gas) kJ/kg · ° C. 1.533 1.359 1.523Heat of vaporization kJ/kg 324.4 1026.7 317.2

[0084] These respective fuels were subjected to a fuel cell systemevaluation test, an evaporative gas test, and a storage stability test.

[0085] Fuel Cell System Evaluation Test

[0086] (1) Steam Reforming

[0087] A fuel and water were evaporated by electric heating and led to areformer filled with a noble metal type catalyst and kept at aprescribed temperature by an electric heater to generate a reformed gasenriched with hydrogen.

[0088] The temperature of the reformer was adjusted to be the minimumtemperature (the minimum temperature at which no THC was contained in areformed gas) at which reforming was completely carried out in aninitial stage of the test.

[0089] Together with steam, a reformed gas was led to a carbon monoxideconversion apparatus (a water gas shift reaction) to convert carbonmonoxide in the reformed gas to carbon dioxide and then the produced gaswas led to a solid polymer type fuel cell to carry out power generation.

[0090] A flow chart of a steam reforming type fuel cell system employedfor the evaluation was illustrated in FIG. 1.

[0091] (2) Partial Oxidation

[0092] A fuel is evaporated by electric heating and together with air,the evaporated fuel was led to a reformer filled with a noble metal typecatalyst and kept at a 1100° C. by an electric heater to generate areformed gas enriched with hydrogen.

[0093] Together with steam, a reformed gas was led to a carbon monoxideconversion apparatus (a water gas shift reaction) to convert carbonmonoxide in the reformed gas to carbon dioxide and then the produced gaswas led to a solid polymer type fuel cell to carry out power generation.

[0094] A flow chart of a partial oxidation type fuel cell systememployed for the evaluation was illustrated in FIG. 2.

[0095] (3) Evaluation Method

[0096] The amounts of H₂, CO, CO₂ and THC in the reformed gas generatedfrom a reformer were measured immediately after starting of theevaluation test. Similarly, the amounts of H₂, CO, CO₂ and THC in thereformed gas generated from a carbon monoxide conversion apparatus weremeasured immediately after starting of the evaluation test.

[0097] The power generation quantity, the fuel consumption, and the CO₂amount emitted out of a fuel cell were measured immediately afterstarting of the evaluation test and 100 hours later from the starting.

[0098] The energy (preheating quantities) necessary to heat therespective fuels to a prescribed reforming temperature were calculatedfrom the heat capacities and the heat of vaporization.

[0099] Further, these measured values, calculated values and the heatingvalues of respective fuels were employed for calculation of theperformance deterioration ratio of a reforming catalyst (the powergeneration amount after 100 hours later from the starting divided by thepower generation amount immediately after the starting), the thermalefficiency (the power generation amount immediately after the startingdivided by the net heat combustion of a fuel), and the preheating energyratio (preheating energy divided by the power generation amount).

[0100] Evaporative Gas Test

[0101] A hose for filling a sample was attached to a fuel supply port ofa 20 liter portable gasoline can and the installation part wascompletely sealed. While an air venting valve of the can being opened, 5liter of each fuel was loaded. On completion of the loading, the airventing valve was closed and the can was left still for 30 minutes.After the can being kept still, an activated carbon adsorption apparatuswas attached to the air venting valve and the valve was opened.Immediately, 10 liter of each fuel was supplied from the fuel supplyport. After 5 minutes of the fuel supply, while the air releasing valvebeing opened and kept as it was, the vapor was absorbed in the activatedcarbon and after that, the weight increase of the activated carbon wasmeasured. Incidentally, the test was carried out at a constanttemperature of 25° C.

[0102] Storage Stability Test

[0103] A pressure resistant closed container was filled with each fueland oxygen, heated to 100° C. and while the temperature being kept as itwas, the container was kept still for 24 hours. Evaluation was carriedout according to “Petroleum products—Motor gasoline and aviationfuels—Determination of existent gum” defined as JIS K 2261.

[0104] The respective measured values and the calculated values areshown in Table 4. TABLE 4 EX. 1 EX. 2 EX. 3 EX. 4 Evaluation resultsElectric power generation by steam reforming method (reformingtemperature = optimum reforming temperature 1)) Optimum reforming ° C.620 610 600 600 temperature 1) Electric energy kJ/fuel kg initialperformance 29000 29190 28070 28260 100 hours later 28980 29170 2804028240 performance 100 hours later 0.07% 0.07% 0.11% 0.07% deteriorationratio Thermal efficiency 2) initial performance 68% 68% 67% 67% CO₂generation kg/fuel kg initial performance 2.983 2.953 3.057 3.075 Energyper CO₂ KJ/CO²-kg initial performance 9722 9885 9182 9190 Preheatingenergy kJ/fuel kg 1307 1322 1176 1184 3) Preheating energy 4.5% 4.5%4.2% 4.2% ratio 4) Electric power generation by partial oxidationreforming method (reforming temperature 1100° C.) Electric energykJ/fuel kg initial performance 14110 14450 12810 12910 100 hours later14100 14440 12790 12900 performance 100 hours later 0.07% 0.07% 0.16%0.08% deterioration ratio Heat efficiency 2) initial performance 33% 34%31% 31% CO₂ generation kg/fuel kg initial performance 2.985 2.954 3.0583.074 amount Energy per CO₂ KJ/CO₂-kg initial performance 4727 4892 41894200 Preheating energy kJ/fuel kg 2033 2091 1879 1883 3) Preheatingenergy 14.4% 14.5% 14.7% 14.6% ratio 4) Evaporative gas test Evaporativegas g/test 12.8 9.2 11.1 10.7 Storage stability test Washed existentmg/100 ml 1 1 2 1 gum EX. 5 Comp. Ex. 1 Comp. Ex. 2 Evaluation resultsElectric power generation by steam reforming method (reformingtemperature = optimum reforming temperature 1)) Optimum reforming ° C.630 460 670 temperature 1) Electric energy kJ/fuel kg initialperformance 29580 18280 29850 100 hours later 29550 18270 29820performance 100 hours later 0.10% 0.05% 0.10% deterioration ratioThermal efficiency 2) initial performance 68% 83% 68% CO₂ generationkg/fuel kg initial performance 3.067 1.529 3.098 Energy per CO₂KJ/CO²-kg initial performance 9645 11956 9634 Preheating energy kJ/fuelkg 1300 1663 1341 3) Preheating energy 4.4% 9.1% 4.5% ratio 4) Electricpower generation by partial oxidation reforming method (reformingtemperature 1100° C.) Electric energy kJ/fuel kg initial performance14280 10650 14380 100 hours later 14260 10640 14370 performance 100hours later 0.14% 0.09% 0.07% deterioration ratio Heat efficiency 2)initial performance 33% 48% 33% CO₂ generation kg/fuel kg initialperformance 3.069 1.530 3.101 amount Energy per CO₂ KJ/CO₂-kg initialperformance 4653 6961 4637 Preheating energy kJ/fuel kg 2008 2533 19883) Preheating energy 14.1% 23.8% 13.8% ratio 4) Evaporative gas testEvaporative gas g/test 3.7 8.1 7.5 Storage stability test Washedexistent mg/100 ml 1 1 1 gum

INDUSTRIAL APPLICABILITY

[0105] As described above, a fuel for a fuel cell system of theinvention comprising a specific amount of oxygenates has performanceswith small deterioration and can provide high output of electric energyand other than that, the fuel can satisfy a variety of performances fora fuel cell system.

1. A fuel for a fuel cell system comprising 5 vol. % or more ofhydrocarbons based on the whole fuel, and 0.5-20 mass % of oxygenates interms of an oxygen content based on the whole fuel, wherein a content ofhydrocarbon compounds having a carbon number of 4 is 15 vol. % or less,a content of hydrocarbon compounds having a carbon number of 5 is 5 vol.% or more, a content of hydrocarbon compounds having a carbon number of6 is 10 vol. % or more, a content of hydrocarbon compounds having carbonnumbers of 7 and 8 in total is 20 vol. % or more, and a content ofhydrocarbon compounds having carbon numbers of 10 or more is 20 vol. %or less.
 2. A fuel for a fuel cell system according to claim 1, whereina sulfur content is 50 ppm by mass or less based on the whole fuel.
 3. Afuel for a fuel cell system according to claim 1 or 2, wherein saturatesare 30 vol. % or more based on the whole hydrocarbons.
 4. A fuel for afuel cell system according to any one of claims 1 to 3, wherein olefinsare 35 vol. % or less based on the whole hydrocarbons.
 5. A fuel for afuel cell system according to any one of claims 1 to 4, whereinaromatics are 50 vol. % or less based on the whole hydrocarbons.
 6. Afuel for a fuel cell system according to any one of claims 1 to 5,wherein a ratio of paraffins in saturates is 60 vol. % or more.
 7. Afuel for a fuel cell system according to any one of claims 1 to 6,wherein a ratio of branched paraffins in paraffins is 30 vol. % or more.8. A fuel for a fuel cell system according to any one of claims 1 to 7,wherein heat capacity of the fuel is 2.6 kJ/kg ° C. or less at 15° C.and 1 atm in liquid phase.
 9. A fuel for a fuel cell system according toany one of claims 1 to 8, wherein heat of vaporization of the fuel is400 kJ/kg or less.
 10. A fuel for a fuel cell system according to anyone of claims 1 to 9, wherein Reid vapor pressure of the fuel is 10 kPaor more and less than 100 kPa.
 11. A fuel for a fuel cell systemaccording to any one of claims 1 to 10, wherein research octane numberof the fuel is 101.0 or less.
 12. A fuel for a fuel cell systemaccording to any one of claims 1 to 11, wherein oxidation stability ofthe fuel is 240 minutes or longer.
 13. A fuel for a fuel cell systemaccording to any one of claims 1 to 12, wherein density of the fuel is0.78 g/cm³ or less.
 14. A fuel for a fuel cell system comprising 5 vol.% or more of hydrocarbons based on the whole fuel, and 0.5-20 mass % ofoxygenates in terms of an oxygen content based on the whole fuel,wherein said fuel has distillation properties of the initial boilingpoint in distillation of 24° C. or higher and 50° C. or lower, the 10vol. % distillation temperature of 35° C. or higher and 70° C. or lower,the 90 vol. % distillation temperature of 100° C. or higher and 180° C.or lower, and the final boiling point in distillation of 130° C. orhigher and 210° C. or lower.
 15. A fuel for a fuel cell system accordingto claim 14, wherein a sulfur content is 50 ppm by mass or less based onthe whole fuel.
 16. A fuel for a fuel cell system according to claim 14or 15, wherein saturates are 30 vol. % or more based on the wholehydrocarbons.
 17. A fuel for a fuel cell system according to any one ofclaims 14 to 16, wherein olefins are 35 vol. % or less based on thewhole hydrocarbons.
 18. A fuel for a fuel cell system according to anyone of claims 14 to 17, wherein aromatics are 50 vol. % or less based onthe whole hydrocarbons.
 19. A fuel for a fuel cell system according toany one of claims 14 to 18, wherein a ratio of paraffins in saturates is60 vol. % or more.
 20. A fuel for a fuel cell system according to anyone of claims 14 to 19, wherein a ratio of branched paraffins inparaffins is 30 vol. % or more.
 21. A fuel for a fuel cell systemaccording to any one of claims 14 to 20, wherein heat capacity of thefuel is 2.6 kJ/kg mass % ° C. or less at 15° C. and 1 atm in liquidphase.
 22. A fuel for a fuel cell system according to any one of claims14 to 21, wherein heat of vaporization of the fuel is 400 kJ/kg or less.23. A fuel for a fuel cell system according to any one of claims 14 to22, wherein Reid vapor pressure of the fuel is 10 kPa or more and lessthan 100 kPa.
 24. A fuel for a fuel cell system according to any one ofclaims 14 to 23, wherein research octane number of the fuel is 101.0 orless.
 25. A fuel for a fuel cell system according to any one of claims14 to 24, wherein oxidation stability of the fuel is 240 minutes orlonger.
 26. A fuel for a fuel cell system according to any one of claims14 to 25, wherein density of the fuel is 0.78 g/cm³ or less.